Single-pipe agricultural irrigation systems comprised of an interconnected series of water sprinkling pipes are used extensively in agriculture, horticulture and golf course maintenance. Typical single-pipe systems emit water from many holes along the entire length of a given pipe series. This is usually accomplished with the aid of hydrostatic pressure delivered by pumps. Hence water and/or other liquids (such as fertilizers) are sprayed or otherwise released into crop growing areas contiguous to the pipe series. However, differences in hydrostatic pressure develop as the series of watering pipes is extended. That is to say, fluid pressure decreases from the pipe nearest the water supply pump to the pipe most remote from that pump. This pressure decrease causes different amounts of water to be released over the length of the pipe series. For example, longer sprinkling distances are created in areas nearer to the water pressure source and shorter sprinkling distances are experienced in areas more remote from that source of water pressure. Concomitantly, those water dispensing holes which are under greater fluid pressure deliver greater volumes of fluid than those at the end of the pipe series.
In most cases it is generally regarded as being undesirable to have different sprinkling rates, volumes and/or spray distances for any given field under cultivation. However, in some cases, field conditions may dictate changes in water requirements. One simple example of this would be the case where one desires to supply more water to an area receiving more abundant sunshine while limiting water delivery to a contiguous shaded area under cultivation with the same crop. Other kinds of problems can arise from water delivery variations. Not the least of these is the fact that some areas may be over fertilized as well as overwatered while other areas are under fertilized and/or underwatered owing to the fact that fertilizing liquids are often mixed in with the irrigation water being dispensed.
For the most part, water uniformity in such single-pipe systems is pursued by adjusting the flow rates and/or pressures of the water being released, use of alternative watering systems and/or movement of individual pipe elements to create other pipe system configurations. Some prior art attempts to better regulate irrigation water flow have employed two or even three main water supply pipes which are interjected at different places in the system in order to try to minimize water pressure differences along the length of a given pipe series. However, use of such multiple main water supply pipes systems implies higher capital cost as well as those higher labor costs implicit in any field modifications of such multi-pipe systems.
Other sprinkling devices employing a single pipe which is divided into two separate chambers have been employed in order to minimize some of the above-noted pressure differential problems. Most of these two-chambered, single pipe systems are comprised of a series of elongated pipes each of which are divided into two distinct chambers by a separator wall running in the pipe's lengthwise direction. Typically, one chamber has a large cross section and the other has a smaller cross section. Hence the large section best serves as a water supply pipe and the smaller as a water dispensing pipe. The supply pipe chamber and the dispensing pipe chamber are placed in fluid communication with each other by a certain number of holes in the interior wall between the chambers for every unit length of pipe. Consequently, any water or other liquid introduced into the water supply pipe flows into the water dispensing pipe through such communication holes and is thereafter sprinkled from other holes in the outside walls of the water dispensing pipe. The size of the fluid communication holes in the interior walls is adjusted from the outside of the pipe by means of adjustment bolts which adjust the flow rate of liquid introduced from the supply chamber to the dispensing chamber. Typically, this is done for every unit length of the double pipe. Hence, the sprinkling distances and/or volumes can be adjusted for each pipe unit.
For each unit length of such two chambered pipe, the supply pipe is open at both of its ends and the dispensing pipe is closed at both of its ends. Hence, where a plurality of such pipes are connected in series to construct a water sprinkling system, the supply pipes are in fluid communication throughout their entire length, while the dispensing pipes for each unit of pipe can be regulated. Again, sprinkling distances, volumes, etc. for each unit length must be regulated by means of adjustment screws for the pipe unit. In practice, adjustments and/or settings of such adjustment screws differ as the distance of a given pipe unit from the source of water pressure is increased.
Unfortunately, these two chamber pipes are very difficult, and hence very expensive, to manufacture. This is especially true in the case of those steel pipes which are typically used in large scale agricultural irrigation systems. Consequently, most two chambered pipes are manufactured by extrusion of synthetic resin materials. However, problems of quality control do occur even when working with extruded synthetic resins. Problems are particularly apt to occur in the cooling of recently extruded resins wherein shrinkage occurs in the separator wall. This shrinkage gives rise to the formation of cracks and separations and, hence, introduces possibilities for leakage from the water supply chamber to the water dispensing chamber. At best then, such synthetic resin, two chambered pipes are only suited to small scale, low pressure, water dispensing systems such as those employed in greenhouses.
Furthermore, since the dispensing pipe chamber is closed at both of its ends for every unit length, it is difficult to inspect and/or clean its inside once the pipe is manufactured. This is a serious drawback because dust and dirt or impurities contained in the liquid being dispensed tend to accumulate in the dispensing pipe. This causes the spurting holes of the dispensing pipes to become clogged, and thereby reduces the effectiveness of the entire sprinkling system.
Some small, low pressure, horticultural scale, two-pipe watering sprinkling systems comprised of two essentially separate pipes also have been developed. A representative system of this type is taught in U.S. Pat. No. 4,162,041. This particular system is generally comprised of a connection socket of a first type including a tubular main pipe connection part and a tubular sub-pipe connection part. The connection parts are united to the pipe at a part of the periphery of each connection part. They are also provided with an internal closure near to their centers. A connection socket of a second type, including a tubular main pipe connection part and a tubular sub-pipe connection part, along with such connection parts, are united to each other at the periphery of each connection pipe. They are placed in fluid communication with each other through an opening at the pipe's central portion. This connection of the second type usually includes a valve for adjusting the amount of liquid passing through the opening from the main pipe to the sub-pipe. Consequently, many "fine adjustments" are required because each valve adjustment is contemplated to operate over a continuous range rather than to operate only in an "on" or "off" mode of operation. Moreover, because all sub-pipes are simultaneously fed from the same main pipe, pressure differentials do develop over the length of such a pipe series if more than one sub-pipe is employed at the same time.
In another version of the liquid sprinkling device of U.S. Pat. No. 4,162,041, the connection parts are united to each other at a part of the periphery of each connection part and communicate with each other through an opening at its central portion. In effect all main pipes are in continuous fluid communication. Consequently, water flow cannot be directed to any particular member of the main pipe series of pipes. The connection socket also includes a valve device, disposed near the opening, for adjusting the amount of liquid passing from the main pipe, through the opening and then flowing in the sub-pipe connection part.
This approach gives satisfactory effects in the context of watering those relatively smaller areas used in horticultural, e.g., greenhouse, activities in that the pressure differences do not greatly affect the spray rates and/or spray differences in these relatively small systems. However, as the length of such systems is increased, as in the case of large scale agricultural operations, such two-pipe systems having continuous flow main pipes, become less and less effective because individual sections of the main pipe cannot be placed in exclusive fluid communication with individual sections of the sub-pipe. In other words, problems arise because the full force of the entire incoming water supply is not delivered directly and exclusively to one water dispensing sub-pipe. Again, this drawback takes on more and more importance as the system is extended farther and farther away from the source of hydrostatic pressure.